Improved methods and apparatus for preparing elasticized thermoplastic yarns



A ril 10, 1962 c. a. EVANS 3,028,653

IMPROVED METHODS AND APPARATUS FOR PREPARING ELASTICIZED THERMOPLASTIC YARNS 2 Sheets-Sheet 1 Filed Dec. 24, 1956 INVENTOR.

CYRIL G. EVANS ATTORNEY April 10, 1962 c, EVANS IMPROVED METHODS AND APPARATUS FOR PREPARING ELASTICIZED THERMOPLASTIC YARNS Filed Dec. 24. 1956 2 Sheets-Sheet 2 INVENTOR. CYRIL G. EVANS ATTORNEY iinite States Patent it A IMPERUVED METHGDS AND APPARATUS FOR PREiARiNG ELASTICIZED THERMOPLAS- TIC YARNS Cyrii G. Evans, Clemson, S.C., assignor to Deering Milliken Research Corporation, Pendieton, N.C., a corporation of Delaware File-d Dec. 24, 1956, Scr. No. 630,325 33 Ciaims. (Cl. 28--1) This invention relates to improved methods and apparatus for elasticizing thermoplastic yarns and is a continuation-in-part of US. application, Serial No. 522,156, filed July 14, 1955, now abandoned.

Elasticized thermoplastic yarns are yarns composed of one or more continuous filaments which have had imparted thereto a relatively permanent tendency to curl, crimp or loop so that when the yarns are formed into fabrics, the fabrics have an elastic nature. The elasticized yarns presently available are of two basically different types. One type of elasticized yarn is torsionally stressed so that the yarn tends to kink or curl to relieve the stresses, while a second type of elasticized yarn is stressed by sharply bending the yarn and thereafter straightening the same so that when it is placed in a tensionless condition it tends to curl or form into loops. Yarns of the first type are commonly referred to as high torque elasticized yarns and yarns of the latter type are commonly referred to as non-torque elasticized yarns-since the elasticization does not primarily depend upon the yarns being torsionally stressed. It is with non-torque elasticized yarns that this invention is concerned.

An early procedure for preparing non-torque elasticized yarns is disciosed in British Patent No. 558,297 and comprises passing a cold end of thermoplastic yarn under a high tension over an unheated deforming member but this early process did not meet with any degree of commercial success for several reasons. In the first place, the tendency of yarn prepared by this process to loop or curl is largely lost by placing the yarn in hot water so that articles or goods .made therefrom lose much of their elasticity upon being washed. In addition, the process of the British patent does not ordinarily result in the yarns having a sufiiciently high degree of curliness or the like to result in an appreciable degree of elasticity in cloth formed therefrom.

In the US. application, Serial No. 274,358, filed March 1, 1952 there is disclosed an improved process for preparing non-torque elasticized yarns and according to this improved process an end of thermoplastic yarn is, while at an elevated temperature, passed around the edge of a blade member under a relatively low tension. The process of this US. application overcomes many of the disadvantages of the process of the British patent and, in particular with certain types of nylon yarns, gives an excellent degree of elasticity which is completely permanent to hot water. With some types of yarn, however, the degree of elasticity which can be imparted by the process of the above US. application is not so great as is frequently desired.

It is an object of this invention to provide improved methods and apparatus for producing thermoplastic yarns with an exceedingly high degree of elasticity and which are eminently suited for use in the manufacture of washable elastic fabrics.

It is another object of the invention to provide a method for producing an excellent degree of elasticity in a wide range of thermoplastic yarns, including yarns to which only a moderate degree of elasticity could be imparted by prior art methods.

The above, as well as other objects of the invention,

are accomplished by the provision of apparatus including means to raise the temperature of a portion of a running length of thermoplastic yarn to thereby reduce the stress necessary to strain the heated portion of the yarn beyond its elastic length, means to stretch the hot yarn beyond its elastic limit to thereby increase its modulus of elasticity and means to pass the hot-stretched yarn under tension through an acutely angular path. By the use of apparatus including this combination of means it is possible to impart a tendency to loop and curl to an end of thermoplastic yarn which is not lost by washing the yarn or fabrics made therefrom in hot water and which, in fact, may actually be intensified by such an operation as will subsequently be described in detail.

The improvement of this invention can, during the bending operation, utilize the high tension and low yarn temperatures of the process of British Patent No. 558,297 or it can preferably embody the improvement of US. ap-

plication, Serial No. 274,358 and employ relatively low'; tension in the yarn and elevated yarn temperatures dur- It is indeed surprising that by the modification of this invention the high tensioning the bending operation.

cold yarn process of the British patent can be transformed into a process whichprovides a yarn with a well de veloped tendency to loop and curl which is reasonably permanent to hot water. Indeed, with polyester yarns the process of the British patent modified according to this invention gives results which, by prior art standards, are generally excellent. However, for best results with all types of yarns, and in particular vwith nylon yarns,

relatively low tensions and elevated yarn temperatures should beutilized in the improved process of this in-.

vention during the bending operation.

The exact reason or reasons for the success of the new process are not fully understood although it is known that a number of changes take place in the fibers of a thermoplastic yarn when it is stretched at an elevated temperature according to this invention. the tension modulus of elasticity of the fibers is.noticeably increased, up to a point, by the stretching operation and it is apparent that this probably is related to the success of the new process in some manner since, in every known instances, best results are achieved when the yarn is hot drawn under such conditions and to such an exv tent as to result in its having within 10 or 20% of the maximum modulus of elasticity which it has been possible to develop in the starting yarn. A second change effected in the fibers of the yarn by the hot stretching operation is that they develop a pronounced brittleness as is evidenced by an appreciable- ,variation in the stress required for rupture of the individual filaments. This also quite obviously is related to the success of the new process since the best and most permanent elasticizing is generally obtained when the yarn is stretched to the extent and under such conditions as to result in the fibers displaying a near maximum degree of brittleness. another change effected by the hot stretching operation is that the elongation to break of the fibers of the yarn is appreciably lowered. This also appears tr be related to the success of the process since best results are obtained, other factors being equal, when the yarn is stretched to the extent necessary to result in the fibers displaying a near minimum elongation to break. The effect of these factors will subsequently be more clearly illustrated.

The yarn to be elasticized according to the new process of this invention can satisfactorily comprise any continuous filamentary strand composed of an organic, hydrophobic, thermoplastic fibrous material. Specific illustrative examples of suitable materials include polyester yarns such as formed from the reaction product of ethylene glycol with terephthalic acid, and nylon yarns such as formed from the reaction product of hexamethylene di- In the first place,

Still" aozaess amine and adipic acid. The invention under certain conditions can also be readily employed for the elasticization of pol'yacrylic fibers formed from polymers of acrylonitrile or from copolymers of acrylonitrile with other related polymeric materials, and for the elasticization of fibers formed esters of cellulose such as cellulose triacetate. Yarns wherein the filaments have a generally circular cross section and a smooth surface are most readily employed and give the most satisfactory results, and some yarns give difiiculty not so much because of their chemical composition or inherent physical properties, but because of the cross-sectional configuration of the fibers. For example, acrylic fibers sold under the name of Orlon have a crosssectional shape which resembles the silhouette of a dumbbell and are difiicult to elasticize by the process of this invention.

Within a selected class of yarns, the yarns most satisfactory for use in this invention are generally those which are commercially available and which are of the types employed in the manufacture of textile fabrics. The starting yarn is preferably one which is partially crystalline and in which the crystallites have been highly orientated by cold drawing or, in other words, by permanently elongating the yarn at'a temperature within about 60 F. of its second order transition temperature. In fact, it is normally preferable to employ a yarn as a starting material which has been cold drawn the maximum possible extent consistent with yarn uniformity, and if one desires to employ a yarn which'is undrawn or which has been cold drawn to less than the practical maximum extent, it is generally advantageous to subject the yarn to an additional cold drawing operation if the yarn has not been annealed or otherwise treated to make such an additional drawing operation impractical; If such a cold drawing operation is, for any reason, impractical, the yarn can still be hot drawn according to this invention but a greater degree of elongation than normal will generally be required since high temperatures, as a general rule, retard alignment of the crystallites; In other words, if hot stretching is resorted to for crystallite alignment, it is generally necessary to stretch the yarn to a considerably greater extent to obtain a near maximum degree of crystallite alignment than would be necessary by a cold drawing operation. There are yarns described in the literature which were reportedly prepared by substituting a hot drawing operation or, in other words a drawing operation conducted above about 250 F., for the cold drawing operation which is normally conducted and such yarns can also generaliy be satisfactorily employed as the starting material in the improved process of this invention.

The denier and filament size of yarns employed in the new process of this invention may vary within wide limits and. in fact, yarns of almost any total denier or filament size can be suitably employed. By way of illustration, the process has been found to give excellent results with the following varied types of yarn: 40 denier 34 filament polyester yarn (Dacron), 100 denier 34 filament nylon (du Pont type 200), 70 denier 34 filament Dacron and denier monofilament Dacron. Under suitable conditions the denier per filament can range from 1 to and the total denier of the yarn can readily be as high as 2,000

or more.

The invention will now be more specifically described with reference to the accompanying drawings in which:

FIGURE 1 is a side elevational schematic view of one form of apparatus according to this invention;

FIGURE 2 is an enlarged view of a portion of the apparatus of FIGURE 1 illustrating the manner in which the yarn is passed about the blade edge;

FIGURE 3 is a front plan view of a portion of the apparatus of FIGURE 1;

FIGURE 4 is an enlarged front plan view of a portion of an apparatus generally similar to that of FIGURE 1 except that provision is made for the yarn to approach and depart the blade edge in a manner which is advan tageous in some instances;

FIGURE 5 is a side elevational schematic view of a portion of an apparatus generally similar to that of FIG- URE 1 except that a modified arrangement is provided for heating the yarn for passage about the blade edge.

With reference to FIGURES l to 3 of the drawings in greater detail, there is illustrated a support member 10 carrying a yarn supply bobbin 12 holding a suitable supply of yarn 14. An end of yarn 16 from the supply on bobbin 12 is withdrawn from the bobbin in an overend manner through a yarn guide 17 positioned on the extended longitudinal axis of the bobbin, in thereafter passes to one section of a duplex yarn advancing means generally indicated by the reference numeral 18.

The yarn advancing means 18 comprises a pair of matching rolls 19 and 20 with roll 19 having a first portion 21 and a second portion 22, generally of different diameters, and with roll 20 having a first portion 23 and a second portion 24 corresponding to the portions 21 and 22 of roll 19. Portions 21 and 22 of roll 19 and portions 23 and 24 of roll 20 are preferably separately formed but, if desired, rolls 19 and 20 can, in each instance, comprise an integral stepped roll. Also, in place of a single duplex yarn advancing means, two simple yarn advancing means can be employed as will subsequently become apparent.

The yarn 16 is passed around portions 21 and 23 of rolls 19 and 23 as sutficient number of turns to insure adequate frictional contact to prevent substantial slippage and thereafter moves to a yarn heater, generally indicated by the reference numeral 26. Yarn heater 26 can be of any suitable type and is illustrated as comprising a plate 28 bent to a radius of about 8 feet so that adequate contact with the yarn end 16 is obtained. The plate 28 is heated by means of an internal electrical resistance heater which is provided with a supply of electric current through leads 30 and 32, and means, not illustrated, are preferably provided to permit the yam heater 26 to be pivoted from operative position when not in use since it is generally not necessary that the yarn be heated at this point.

From heater 26 the yarn end 16 passes to a second yarn advancing means, generally indicated by the reference numeral 33, and which comprises a pair of rolls 34 and 36. Means are provided for heating at least an annular portion of the peripheral surface of roll 34 and this heating means may take any suitable form. For example, this heating means may comprise a stationary annular electric heater positioned on the inside of roll 34 in close proximity to the inner face thereof. A pair of leads 37 and 33 are provided for supplying electric current to the heater within roll 34.

Positioned closely adjacent a heated annular portion of the peripheral surface of roll 34 is a roll 39 which is preferably formed with a smooth metal peripheral surface, and extending into the bite between rolls 34 and 39 is a blade member 40 having a sharpened edge 41. After being passed several turns about rolls 34 and 36, the yarn end 16 is withdrawn from roll 34 to roll 39 and passes in an acutely angular manner (see FIGURE 2 of the drawings) about the edge 41 with the edge disposed at the apex of the acute angle in the yarn path. The blade 40 is retained in position by a suitable blade holding means 42 which is preferably formed of a heat conductive metal and which preferably has a relatively large mass compared to that of the blade member 40 so that the blade member is retained at a temperature which is low relative to that of roll 34. Means, not illustrated, are preferably provided to permit the blade holder 42 and blade 40 to be pivoted from operative position for purposes of threading.

From roll 39, the yarn end 16 is passed over an oiling roll 43 to the second section of yarn advancing means 18 and is passed one or more turns about portions 22 and 24 of rolls 19 and 20. The purpose of oiling roll 43 is to apply a lubricant to the yarn so that it can be knit directly from the package on which it is collected. The yarn is then passed from roll 20 about a guide pulley 44 and through a guide 46 to a take-up means, generally indicated by the reference numeral 48. The take-up means 48 may be of any suitable type and is here illustrated as comprising a conventional ring and traveler array. Generally it is desirable to insert a small amount of twist into the yarn at this point so that a ring and traveler take-up means is advantageous but if it is not desired that twist be inserted, some other type of yarn take-up device should, of course, be employed.

Driving means, not illustrated, are provided for driving at least one roll of each of yarn advancing means 18 and 33 and, if desired, both rolls of each of the yarn advancing means may be driven in such a manner that they have the same surface speed. Normally, however, it is advantageous to drive only the larger of the two rolls in each of the yarn advancing means and allow the smaller of the two rolls, in each instance, to idle freely. The yarn advancing means 18 and 33 should be driven in fixed timed relationship to each other so that the amount that the yarn is stretched or is allowed to contract in passing from one yarn advancing means to the other is substantially constant. If desired, the driving means may include a variable ratio means to change the relative rate of rotation of the rolls in the two yarn advancing means but this is not normally required, since various relative rates of yarn advance can readily be achieved by substituting rolls of various diameters in the two yarn advancing means. Norm-ally the rate of rotation and the roll diameters should be such that the yarn is stretched in passing from the first section of yarn advancing means 18 to yarn advancing means 33 and such that the yarn is allowed to contract or, at least is not stretched in passing from yarn advancing means 33 to the second section of yarn advancing means 18.

Driving means, not illustrated, is also preferably provided for roll 39 so that it can be driven to have a surface speed slower, faster or equal to the surface speed of roll 34 and in addition to serving as a guide means to cause the yarn to follow an acutely angular path about the edge of blade member 40, the roll 39 can serve at least two additional functions. First, the roll 39, if it is formed of a heat conducting material, can serve to cool the yarn immediately following its contact with the edge 41 and secondly, the roll 39 can be employed to assist in controlling the tension in the yarn as it passes about the edge 41 of blade 40. If the roll 39 is driven such that it has a surface speed exactly equal to the surface speed of roll 34, the tension in the yarn passing about edge 41 is delermined primarily by the tendency of the yarn end 16 to contract after being released from the high tension employed to stretch the same, but by driving roll 39 so that it has a surface speed in excess of the surface speed of roll 34, the tension in the yarn passing about the edge 41 can be increased or by driving the roll 39 so that it has a surface speed less than the surface speed of roll 34, the tension in the yarn can be decreased. The surface speed of portion 22 of roll 19 relative to the surface speed of roll 34 will also have an effect on the tension in the yarn passing about the blade edge since the relationship of these two surface speeds determines the amount that the yarn is allowed to contract in passing from yarn advancing means 33 to the second section of yarn advancing means 18, and the force with which the yarn tends to contract decreases as the amount of contraction permitted increases. It will be seen, therefore, that the tension in the yarn passing around the blade edge can be varied by: (1) varying the surface speed of roll 39 relative to the surface speed of roll 34; (2) varying the surface speed of portion 22 of roll 19 relative to the surface speed of roll 34; (3) varying frictional characteristics of the surface of roll 39.

In operation, an end of yarn from supply package 12 is threaded through the apparatus in the manner previously described. If it is desired that the yarn be passed about the edge of blade member 40 while at an elevated temperature, the yarn heater within roll 34 is brought to a proper temperature by supplying a selected amount of current through leads 37 and 38, and if the temperature at which the yarn is to be passed about the edge is approximately the same as the temperature at which the yarn is to be hot stretched, yarn heater 26 need not be energized and can be removed from operative position. Under these conditions, stretching of the yarn occurs predominantly atthe point where the yarn comes into contact with the surface of roll 34. If it is desired that the yarn be stretched more than a few percent, rolls 34 and 36 may have correspondingly tapered peripheral surfaces and part or all of the stretching of the yarn can be accomplished during the time that the yarn makes its several turns about these two rolls. If it is desired that the yarn be passed cold about the edge 41 of the blade to, the heater within roll 34 should not be energized and in this instance heater 26 is brought to a proper operating temperature by a supply of electric current through leads 3t and 32. When the yarn heater or heaters are at a proper temperature, the apparatus is placed in operation and requires no further attention unless a yarn end breaks or the yarn supply 14 becomes depleted.

While only a single position has been illustrated, it will be readily apparent to those skilled in the art that the.

apparatus is so designed that a single frame may embody a plurality of positions and, in fact, a multi-posi-tion ap paratus according to this invention can readily be constructed by modification of a conventional twister frame such as that manufactured by Universal Winding Company and designated as the Atwood Model l0-B Twister. To accomplish such a modification it is only necessary to add to the frame, for each position, the two yarn advancing means, the blade holding means, the roll 39 and the various yarn heaters.

VJith particular reference to FiGURE 4 of the drawings, there is illustrated a modified arrangement wherein the yarn approaches and departs the blade edge ..at an angle, in each instance, in a plane parallel to the edge. This is advantageous in some instances as will subsequently be explained. in this embodiment of the aparatus, an end of yarn 16' passes from a roll 34, which corresponds to roll 34 of yarn advancing means 33 in the apparatus of FIGURES 1 to 3, and is transported in an acutely angular path about the sharpened edge of a blade member iii. The yarn thereafter passes in a partial wrap about roll 39' which corresponds to and performs the same functions as roll 3? in the apparatus of FY- URES l to 3. Although the axis of rotation of roll 34, the longitudinal axis of the sharpened edge of blade 48 and the axis of rotation of roll 3? lie in generally.

parallel vertical planes, the longitudinal axis of the edge of blade 46 is inclined withrespect to the axis of rotation of roll 34, and the axis of rotation of roll 39 is further inclined with respect to the longitudinal axis of the edge of blade 4.0. This results in the yarn being guided by rolls 34 and 35" in such a manner that it is skewed about the edge of blade 40 as is clearly illus tratcd in FIGURE 4 of the drawings. The angles of approach and departure of the yarn with respect to the blade edge in planes parallel to the edge can readily be varied by changing the angle at which the longitudinal axis of blade 4 is inclined relative to the axis of rotation of roll 34 and by changing the angle at which the axis of rotation of roll 39 is further inclined with respect to the longitudinal axis of the edge of blade 4t). A yarn guide 5% is provided so that the yarn 15 can be passed in a vertical plane to the next component of the apparatus.

in FIGURE 5 of the drawings there is illustrated a modified form of apparatus which has the advantage, in some instances, that the yarn can be more readily skewed about the blade edge. In this embodiment of the invention a yarn end 16" is passed about a duplex yarn advancing means 18" which corresponds to the duplex yarn advancing means 18 in the apparatus of FIGURES l to 3 of the drawings. The yarn then passes about a yarn heater 26 to a second yarn advancing means 33" and thereafter passes through a guide 52 to a second yarn heater 54. The yarn heater 54 is illustrated as comprising a flat strip of heat conductive material with a slightly arcuate yarn engaging upper face and is retained at an elevated temperature by any suitable means. The heater t in this embodiment of the invention corresponds to the beater within roll 34 of the apparatus of FIGURES l to 3 and performs the same functions except that it cannot readily be employed to heat the yarn for the hot stretching operation and heater 26" must normm'ly be employed for this purpose.

A blade member 48" is so positioned that its edsze extends in close proximity to one side edge or" the heater S-l and the yarn passes from heater 54 in an acutely angular path about the edge of blade 43 with the edge of blade 40" positioned at the apex of the acute angle in the yarn path. The yarn 16 then passes in a partial wrap about the peripheral surface of a roll 39", which corresponds to roll 39 of the apparatus of FTGURES l to 3 and periorrns the same function as roll 39 in the earlier described apparatus, and thereafter passes through a guide 56 to yarn advancing means 11%". The yarn then passes about a guide puiley -.--i and to a take-up means, not illustrated.

The operation of the apparatus of FEGURE 5 of the drawings is generally similar to the o eration of the apparatus ol FiGURES l to 3 of the drawi except that yarn heater 26 is normally employed for the hot stretching operation whereas in the apparatus of FIGURES l to 3 the yarn heater 26 is only infrequently employed. A further distinction is that the apparatus of FlG-URE 5 provides a simple means for skewing the yarn about the blade edge and if one desires to awomplish this result it is only necessary for yarn guides 52 and 56 to be placed in dillcrcnt vertical planes transverse to the axis of rotation of roll 39". The angles of approach and departure of the yarn to the edge of blade 46 in planes parallel to the edge can then readily be controlled by varying the distance between the vertical planes transverse to the axis of rotation of roll 39" in which the yarn guides 52 and 56 are placed.

The degree of hot stretching required for the most satisfactory results in the new process of this invention will depend upon the nature of the specific yarn being employed, and even for yarns of the same chemical composition, the optimum degree of stretching may vary because of different conditions being employed in their manufac ture. As previously mentioned, most commercially available yarns have been cold drawn a near maximum possible extent during manufacture to result in a high degree of molecular orientation and the degree of hot stretching required for best results with such yarns is generally from 3 to 2 0%. With yarns that have been cold drawn less than a near maximum, the degree of hot stretching for best results is generally in excess of the above figures and for substantially undrawn yarn the degree of hot drawing for best results may be several hundred percent. For yarns that have been hot drawn during manufacture, the degree of hot stretching necessary for best results in the process of this invention is frequently less than the above figure and may, for example, be only from about 1 to 3%. For any given yarn, a near optimum degree of hot stretching can be readily determined by a simple test which comprises drawing the yarn, while at a temperature within a preferred range to be subsequently defined, to determine the amount of elongation necessary to result in the fibers of the yarn having a near maximum tension modulus of elasticity, the lowest elongation to break and/or a maximum brittleness. As a guide it has been found that the polyester yarn available under the trademark Dacron is pre erably s;retched from 4 to 7%.

with the optimum being approximately 5%. The polyamide (poly-hexamethylene adipamide) yarn sold by E. I. duPont de Nemours Company as nylon type 200 is preferably stretched 5 to 15% with the optimum being about 12%, and the polyamide (poly-caprolactam) yarn sold by American Enka Company under the trademark Nylenka is preferably hot stretched 5 to 15% with the optimum being about 9 /2%.

The temperature to which the yarn is heated for the stretching operation may be varied within reasonably wide limits and this is particularly true in instances where the yarn is passed about the blade edge under a relatively low tension and at an elevated temperature. Under such conditions, a degree of operativeness may be achieved with most yarns by employing for the hot stretching operation a temperature which is about 180 F. below the sticking temperature of the yarn, and with nylon yarns operative results can be obtained with temperatures as much as 270 F. below the sticking temperature. For example, with nylon type 66 and nylon type 6 operative results can be achieved when employing any temperature above about 180 F. for the hot stretching operation, but with polyethylene glyeol-terephthalate yarns a temperature at least above about 270 F. should be employed in all instances. When the yarn is to be passed about the blade edge cold (i.e. below about -l75 F.) and under a relatively high tension, the temperature for the hot stretching operation is more critical and higher temperatures must generally be employed for satisfactory results. For example, with nylon type 66 it is generally necessary to employ a temperature for the hot stretching operation, for satisfactory results under these conditions, of at least about 275 F., for nylon type 6 it is generally necessary for satisfactory results to employ a temperature of at least about 215 F., and for polyethylene glycol-terephthalate yarns it is generally necessary. for satisfactory results under these conditions to employ a temperature for the hot stretching operation of at least about 370 F. As a rule it is advantageous to employ a considerably higher temperature than the above minimums for the hot stretching operation. Good results can generally be obtained at temperatures closely approaching the sticking temperature of specific yarn being processed, but it is not a rule that the higher the temperature the etter the results since one eventually reaches a temperature with each specific yarn where no marked improvement in results is obtained by employing higher temperatures. For nylon type 66 yarns the temperature above which no marked improvement in results can readily be obtained is about 390 F., with nylon type 6 yarns the temperature is about 320 F. and with polyethylene glyeol-terephthalate yarns the temperature is about 400 to 430 F. Since high temperatures generally result in some degradation of almost all yarns, it is gen erally advantageous to hot stretch the yarn at or slightly below these temperatures so that the preferred temperature range for nylon type 66 is usually from about 280 to 390 F., the preferred range for nylon type 6 is from about 240 to 320 F. and the preferred range for polyethylene glyeol-terephthalate yarns is usually from about 370 to 430 F.

The temperature of the yarn at the time it contacts the blade edge may vary from room temperature to substantially the sticking temperature of the yarn being processed but, as a general rule, elevated temperatures should be employed and this is particularly true with respect to all yarns other than polyethylene glycol-terephthalate yarns. By employing elevated temperatures one can, with most yarns, impart a degree of crimp that is several times greater than the degree of crimp that can be imparted by passing the yarn to the blade edge at substantially room temperature and, in addition, the crimp imparted at elevated temperatures generally has a slightly higher degree of permanency. The outstanding exception to this rule is polyethylene glycol-terephthalate yarns and with this type of yarn, the results obtainable by the use of elevated temperatures during the bending operation are only slightly improved as compared to the results that can be achieved by passing the yarn to the blade edge in an unheated condition so that it passes about the edge at a temperature to which it is heated only as a result of friction. The preferred temperature range for the yarn to be passed to the blade edge is generally from about 200 to 425 F. and more specifically is from about 280 to 360 F. in the case of nylon type 66 yarns, from about 240 to 340 F. in the case of nylon type 6 yarns, and from about 280 to 425 F. in the case of polyethylene glycoLterephthalate yarns.

The tension under which the yarn is passed over the blade edge can also vary within wide limits and the most advantageous tension in any instance is determined by a number of variables. For example, the composition of the specific yarn being processed, the cross-sectional configuration of the yarn, the radius of curvature of the blade edge and the grain structure of the blade will all affect the operative and preferred ranges for tension, but the most important variable to be considered in determining an advantageous tension is the temperature of the yarn being passed to the blade edge. As a general rule, if the yarn is hot (i.e. above about 180 F), best results are obtained with relatively low tensions and if the yarn is cold, best results are obtained by employing relatively high tensions. With the yarn at an elevated temperature at the time it is passed about the blade edge, the operative tension range extends from about 0.05 gram per denier to substantially the elastic limit of the specific yarn being processed at the temperature to which the yarn. is heated, or, in other words, approximately 1 gram per denier with most yarns, and the preferred tension range is from about 0.1 to 0.4 gram per denier. When the yarn being passed about the blade edge is unheated, the operative tension range is generally from about 0.4 to 3 gram per denier and the preferred range is generally from about 0.7 to 2.5 I

gram per denier. With the yarn hot, the optimum tension is generally the lowest tension under which uniformly good contact of the yarn with the blade edge can be obtained and with unheated yarn, the optimum tension is generally substantially the maximum at which the particular yarn can be passed about the blade edge without an objectionable number of yarn breaks. A possible reason for this difference will be subsequently explained.

In instances where the yarn is to be passed around the blade edge at an elevated temperature, the blade edge should be positioned as closely to the yarn heater as is possible in all but exceptional instances. As previously mentioned, elevated temperatures generally result in a measure of deterioration in any yarn so that it is desirable that the yarn be heated to the minimum temperature consistent with the results desired and by placing the blade edge exceedingly close to the yarn heater, substantially no cooling of the yarn occurs prior to the time it contacts the blade edge. If the blade edge is removedfrom the yarn heater even as much as A: of an inch, the temperature of the yarn will drop appreciably during the time that the yarn is passing from the yarn heater to the blade edge so that it will be necessary to heat the yarn to a temperature sufficient to compensate for this drop and this will normally result in unnecessary yarn deterioration. The only instances in which it is advantageous for the blade edge to be removed any substantial distance from the yarn heater occur when one desires to pass the yarn to the blade edge at room temperature or when one is employing the same yarn heater to heat the yarn for the hot stretching operation and for the bending operation and it is desired that the yarn be hot stretched at a temperature in excess of that at which it is passed to the blade edge. In these instances, the most advantageous distance for the blade edge to be placed from the yarn heater depends upon the temperature differential desired for the hot stretching and bending operations and if the yarn is to be passed about the blade at substantially room temperature,

' edge.

10 the blade may be spaced from the yarn heater any convenient distance.

In instances where the yarn is passed to the blade edgeat an elevated temperature, cooling of the yarn should be effected as soon as possible after the point at which the yarn contacts the blade edge. in fact, best results are generally achieved if the yarn is cooled during the actual bending thereof and this efifect can readily be achieved by retaining the blade member at a temperature which is low relative to that of the yarn heater. In any instance, and in particular where no effort is made to retain the blade member at a relatively low temperature, better results are generally achieved if the yarn is posi: tively cooled immediately after its contact with the blade This can be accomplished by directing a blast of cold air against the yarn, by passing the yarn in surface contact with a cold heat conducting member or, in

instances Where the blade is retained at a low tempera-.

ture, by passing the yarn in contact with one face of the blade member. Any degree of cooling in this segment of the yarn path generally gives improved results and for best results, the yarn should be cooled below about F. as rapidly as possible following its departure from the blade edge.

When elevated temperatures for the yarn are employed in the bending operation, the yarn is preferably allowed to contact as it is passed about the blade edge and, as a general rule, best results are obtained when the yarn is allowed to contract substantially the maximum possible extent in this portion of the yarn path. With most nylon yarns, it is possible to over-feed the yarn to the.

blade edge at least about 5 to 8% and excellent results are achieved with this degree of over-feed. With poly ester yarns, an even higher percentage of over-feed is generally possible and, for example, one can frequently.

over-feed a polyester yarn to the blade member in an amount of from about 10 to 15%. a near optimum degree of over-feed can readily be determined by trial and error since if the degree of over-feed is too great, the yarn simply becomes slack in the vicinity of the blade and refuses to run. ation is conducted on cold yarn, it is, as previously mentioned, generally not advantageous to allow the yarn to 7 contract as it is passing about the blade edge, but a small degree of contraction in a subsequent portion of the yarn path may frequently be advantageous. This result can readily be accomplished in the apparatus illus-;

trated in the drawings by driving the roll 39 with a surface speed in excess of the linear speed of the yarn so that the yarn is under a higher tension as it passes around,

the blade edge than it is in the portion of the yarn path immediately following roll 39.

It is not known with certainty why better results are obtained when hot yarn is passed about the blade edge under a relatively low tension and allowed to contract while better results are obtained with cold yarns by passing the yarn around the blade edge under a relatively high tension and under such conditions that the yarn is prevented from undergoing any appreciable degree of contraction. T he most logical explanation appears to be that there are two different phenomena involved in the elasticizing procedure of this invention, and that both of these phenomena have a positive elfect upon the overall elasticity of the processed yarn. The first of these phenomena would appear to be shrinkage of the face of the yarn which passes in contact with the blade edge and the second would appear to be stretching of the face of the yarn remote from the blade edge. It would further appear that the first of these phenomena is moreeffective in producing a high degree of elasticity than the second if the process is conducted under such conditions that a high degree of shrinkage of one face of the yarn can occur and that heat is one of the necessary conditions. Therefore, if hot yarn is being processed, one should concentrate upon obtaining a maximum degree With any given yarn,

When the bending oper-,

of shrinkage of the face of the yarn in contact with the blade but it cold yarn is being processed, an effective degree of shrinkage of one face of the yarn cannot readily be achieved and one should concentrate upon obtaining the maximum degree of stretching of the face of the yarn remote from the blade. All available evidence indicates that the above explanation is correct but applicant wishes to emphasize that it is only theory and that he does not Wish his invention to be limited thereby.

Inasmuch as the blade edge exerts appreciable forces on the yarn being passed thereover, best results are generally obtained if the yarn is lubricated at the time it is passed about the blade edge and this is especially true with yarns other than nylon which do not have the low coefficient of friction with which nylon is characterized. Any suitable yarn lubricant may be employed although it is generally preferable to employ one which can be readily removed followin' the elasticizing procedure and suitable examples include low viscosity mineral and vegetable oils and esters of fatty acids such as sorbitol tripalmitate. The oil is best applied to the yarn by capillary action or by means of a felt wick at a point in the yarn path immediately preceding its contact with the acuate edge.

The radius of curvature of the acutely angular portion of the yarn path, or in other words the radius of curvature of the blade edge, is an important consideration and, as a general rule, should be as small as possible without resulting in an excessive number of yarn breaks. it the blade edge is too blunt, the degree of elasticity in. the finished yarn will not be as high as is desired, but if the edge is too sharp, the yarn will frequently be severed and will not run in a satisfactory manner. The minimum blade edge radius of curvature which can satisfactorily be employed depends upon a number of factors including the composition of the particular yarn being processed, the temperature of the yarn, the size of the filaments or filament in the yarn, the grain size of the material from which the blade is formed and the tension in the yarn passing about the blade edge. It is a general rule that the mean radius of curvature of the blade edge can suitably be less with yarns composed of relatively small diameter filaments than with yarns composed of relatively large diameter filaments and it is also a rule that a blade member having an edge with a smaller radius of curvature can be employed when the yarn passing about the edge is under a relatively low tension and is at a relatively high temperature than can be employed when the yarn passing about the blade is under a relatively high tension and at a relatively low temperature. Further, a blade member having a considerably smaller radius of curvature can, other conditions being equal, be employed with nylon yarns than can be employed with other types of yarns. With all conditions favorable, one can satisfactorily employ a blade member having an edge radius of curvature equal to not more than about 0.05 times the diameter of the yarn filaments which means that in exceptional instances the radius of curvature may be as small as l or 2 microns; however, best results are usually obtained when the radius of curvature of the blade edge is equal to at least about 0.0! times the dial eter of the yarn filaments. In other words, it is generally preferred, even with nylon yarns, to employ a blade having an edge with a radius of curvature of at least 3 to 6 microns, and with unheated polyester yarns it is generally preferred that the blade edge have a radius of curvature of at least about 10 to microns. The maximum radius of curvature which can generally be employed with satisfactory results is from about 2 to times the filament diameter and when a blade with a larger radius of curvature than this is employed, the yarn, as a general rule, will not be stressed to a sufficient degree to give a completely satisfactory measure of elasticity.

The angles of approach and departure of the yarn to and from the acuate edge in a plane transverse to the axis of the edge are not critical and may vary to such an extent that the total of the angle of incidence and the angle of departure is equal to as much as or these angles may be so small that the yarn is led through as near a 180 turn as the thickness of the blade will permit. As a general rule, best results are obtained when the included angle between the yarn approaching the blade edge and the yarn departing from the blade edge is less than about 70. The angle of departure can, in many instances, and in particular when a monofilament yarn is being processed, advantageously be considerably smaller than the angle of incidence. For example, best results have been obtained when the angle the departing yarn makes with the plane of the blade is as small as practical out, in order to reduce the multiplication of tension fluctuations in the approaching yarn while it is passing around the blade, the angle of approach can, in most instances, advantageously be 24 or more. With multifilament yarns, the angle of approach and departure of the yarn to the acuate edge in planes parallel to the edge is also important since by skewing the yarn relative to the axis of the blade edge, one can facilitate the passage of broken filaments over the edge. Best results have been achieved when a multi-filament yarn is passed about the edge of a blade in such a manner that an imaginary plane through the approaching yarn and perpendicular to the plane of the blade intersects a second imaginary plane, also perpendicular to the plane of the blade and passing through the departure yarn, at an angle of from about 40 to 100. With monofilament yarn it is generally advantageous for the yarn to approach and to depart from the blade edge in a plane which is substantially perpendicular to the blade edge, except that, in some instances, it may be advantageous to have a small angle between the approaching and departing yarn in the plane of the blade to impart a small degree of torsional stress to the yarn.

The linear velocity of the yarn over the blade edge may vary within extremely large limits and, for example, may range from about 1 to 2,000 feet per minute or higher. The yarn velocity, of course, affects other process variables and as the yarn velocity increases it becomes increasingly difiicult to maintain the yarn at a proper temperature and under a proper tension at the time it contacts the blade edge and to maintain the yarn at a proper temperature during the hot stretching operatron. Normally, because of apparatus limitations, the preferred range for the linear speed of the yarn is from about 200 to 600 feet per minute.

The yarn, after its contact with the acuate edge, displays a measure of loopiness or curliness when in an untensioned condition but, to develop the full elastic nature of the yarn, it must be given a heat treatment. This is because the yarn contains latent stresses potentially urglng it to assume a convoluted linear configuration and these stresses are released by the heat treatment. The heating operation can, if desired, be conducted before the yarn 1s formed into fabrics by passing a running length of the yarn into contact with a heater element or through a heated fluid under such conditions that the yarn is free to contract; however, if the full elastic nature of the yarn is to be developed subsequent to knitting or weaving, it is best performed by agitating the fabric while gradually raising the temperature of the same ac cord ng to the disclosure of co-pending United States application, Serial No. 512,871, filed June 2, 1955, now abandoned. Any degree of heating will generally be beneficial but for best results, the yarn, either before or after weaving or knitting, should be raised to a temperature of at least about F. and preferably at least about F. with the yarn in a substantially tensionless condition. Higher temperatures are not detrimental and the yarn or fabrics made therefrom may be heated to a temperature approaching the softening point of the 13 yarn without deleterious results as long as the yarn is retained in a slightly tensioned or tensionless condition during such times as it is at an elevated temperature.

The invention will now be illustrated by the following specific examples:

EXAMPLE 1 A 70 denier 34 filament zero twist polyester yarn was heated to 430 F. and stretched varying amounts of from 1 to 10%. The results of the hot stretching operation on the physical characteristics of the yarn were then determined and are given in the following table. All figures given are approximate and are averages for 10 different tests. All determinations were made at 70 F. and 65% relative humidity.

Table I Average Average Tension Variation of Elongation Modulus of Stress in gms. Percentage Stretched to Break in Elasticity in Required for Percent gmsJden. at Rupture in 10 3 gms./denier Tests Stress The yarns hot stretched as above were passed at room temperature over a blade having an edge with a radius of curvature of 0.004 inch at a linear speed of 100 yards per minute. The yarn was passed around the blade as sharply as possible so that it was in contact with both the top and bottom surfaces thereof and the tension in the yarn following its contact with the blade .was determined to be 2 gms. per denier. The best elasticizing was obtained when the yarn was stretched 5% and it will be noticed that this coincides with the point at which the yarn approached the highest modulus of elasticity, the point at which the yarn had the lowest average elongation to break, and the point at which it had the greatest brittleness as indicated by the variation in stress necessary to rupture the yarn in a total of 10 tests. Excellent results were obtained when the yarn was stretched from 4 to 7% and fair results were obtained in all other instances. Even when the yarn was stretched as near' to 0% as possible at 430 F., operative results were obtained which indicates that only a very slight degree of stretching is necessary with polyester yarns. When yarn as received from the manufacturer was similarly processed, substantially no elasticization whatsoever was obtained.

EXAMPLE 2 A sample of 70 denier, 34 filament, one half turn Z twist, Du Pont nylon type 200 yarn was stretched varying percentages at 400 F. The physical characteristics of the yarn were then measured as in the preceding example and the results are given in the following table:

Following the determination of the physical characteristics of the yarn, it was passed at room temperature about an acute edge having a radius of curvature of 0.002 inch at a linear rate of yards per minute. The angles of approach and departure in a plane transverse to the plane of the blade were as small as the thickness of the blade would permit so that the yarn was in contact with the blade both before and after being drawn around the acute edge. The angle between the approaching and departing yarn in the plane of the blade was approximately 85. At least some degree of elasticizing was obtained with all percentages of stretch but best results were obtained with yarns stretched 10 to 16%. A very distinct optimum was found at 12% stretch and it will be seen from the above table that the yarn developed a dis tinct brittleness at this point. Although the tension modulus of elasticity continued to increase slightly after the optimum stretch had been achieved, the rate of increase was noticeably less after the yarn had been stretched the minimum preferred amount. Also, it will be noticed that at the optimum stretch, the elongation togbreak was in 1% of the minimum.

EXAMPLE 3 American Enka during manufacture.

A bobbin of the hot-stretched standard production Nylenka yarn described above was placed upon a Universal Winding Company Model 10B down-twister equipped for the edge elasticizing of thermoplastic yarns and an end of yarn from the bobbin was passed first through a gate-type tension regulator, over the surface of a one and one-half inch heater strip maintained at a temperature of about 330 F., about the edge of a strip of 0.0005 inch thick shim stock in an acutely angular path so that the included angle between the approaching and departing yarn was approximately 25, and thereafter to a yarn collective means. The tension regulator was adjusted to provide a tension in the yarn, measured immediately folowing contact of the yarn with the shim stock edge, of 5 grams and the yarn was passed about the edge at the rate of 40 yards per minute. A skein ofjthe processed yarn was formed from yards by winding the yarn on a reel of 56 inch circumference, thus giving a skein length, when the yarn was removed from the reel and extended, of about 27 inches. The skein was then loaded with a 3.25 gram weight, suspended in water at a temperature of F. and the length of the skein measured.

A bobbin of the hot-stretched Nylenka yarn, which had been cold drawn an extra 10% during manufacture, was placed upon the same position of the same twister and passed about the same blade edge at the same linear rate and under substantially the same tension. The length of a skein of the processed yarn was then measured in the same manner as described above.

For comparative purposes, a bobbin of each of the above described yarn samples, which had not been hot stretched, was placed on the same position of the same down-twister employing the same conditions and the same piece of shim stock as a blade member. Skeins of the two yarns were then made and length determinations performed in the manner described above.

The results of all of the'above tests are given in the following table:

It will be seen from the test results that cold drawing of type 6 nylon yarn an additional 10% had no measurable effect on the degree of crimp that could be imparted by passing a heated end of the yarn about a sharp edge and that the test skein length obtained with commercial type 6 nylon yarn was the same as obtained with the specially processed type 6 nylon yarn. It will also be seen that a marked increase in the degree of crimp imparted was obtained by hot stretching either of these two yarns 10% as a preliminary step. In fact, the amount of crimp in the hot stretched samples was approximately 400% greater than that in the yarn samples not hot stretched since a skein of type 6 nylon, as described above will, as a result of thermal contraction, shrink about four inches when immersed in water at 140 F.

EXAMPLE 4 Several different samples of three different yarns were processed by different methods to determine the relative merits of each method. The first type of yarn processed was 15 denier monofilament type 200 nylon 66 produced by E. I. du Font and this yarn was given three separate and distinctive treatments as follows:

(1) Raw nylon 66 yarn as received from the manufacturer was passed at 40 yards per minute about a one and one-half inch heater strip maintained at a temperature of about 315 F. and thereafter about a blade edge having a mean radius of curvature of about 0.0025 inch. The blade edge was placed in close proximity to the heater so that the yarn passing about the blade edge was at substantially the same temperature as the heater and the yarn was maintained under a tension of approximately 4 grams measured immediately following its contact with the blade edge. This is essentially the process of US. application No. 274,358 above mentioned.

(2) Same as process No. 1 except that the temperature of the heater adjacent the blade edge was approximately 325 F. and the yarn was hot stretched 10% at a temperature of 400 F. prior to being passed about the blade edge.

(3) The yarn was hot stretched 10% at a temperature of 400 F., Esso Mineral Seal Oil was wicked onto the yarn immediately preceding its passage about the blade edge, the yarn heater adjacent the blade edge was unheated so that the yarn was passed to the blade edge at room temperature, and the yarn was passed about the blade edge under a tension of approximately 30 grams. The mean radius of curvature of the blade edge was approximately 0.0005 inch.

The following procedures were employed in processing 15 denier monofilament Nylenka type 6 nylon produced by American Erika:

(4) Same as process No. 1.

(5) Same as process No. 2 except that the heater adjacent the blade edge was maintained at a temperature of about 300 F. and the yarn was hot stretched at 300 F.

(6) Same as process No. 3.

The following procedures were used in processing denier monofilament Dacron produced by E. I. du Pont:

(7) Same as process No. 1 except that a nine inch heater strip maintained at a temperature of approximately 16 325 F. was employed and the yarn was drawn about the blade edge at a rate of 31 yards per minute.

(8) Same as process No. 7 except that the yarn was hot stretched 5% at a temperature of 300 F. before being passed about the blade edge, the heater strip was ten inches in width and the yarn was passed about the blade edge at about 32 yards per minute.

(9) Same as process No. 8 except that the yarn was hot stretched 5% at 400 F.

(10) Same as process No. 3 except that the yarn was hot stretched 5% at 300 F.

(11) Same as process No. .10 except that the yarn was hot stretched 5% at 400 F.

Following all tests with all three types of yarns, skeins were prepared on a reel as described in Example 2 ex- .cept that only about 62 yards of yarn were employed in making each skein so that the skein, in each instance, con tained 40 complete turns of yarn. The length of the skein, in each instance, was measured immediately upon removal from the reel and while the 40 turns of yarn were under a total tension of 1.63 grams. In the case of nylon 66 and nylon 6 samples, the crimp in the yarn was developed by immersion of the skein in hot water at 140 F. and the length of the skein, weighted with a 1.63 gram weight, was then measured, in each instance, with the skein and weight immersed in water. In the case of Dacron yarns, the heat development was carried out under tensionless conditions in a dry air oven maintained at difierent temperatures to be subsequently specified. The yarn was maintained in the.oven for approximately one minute and the skein thereafter weighted with a 1.63 gram weight and its length in air measured.

The results of afirst series of tests as above described are summarizedin the following table:

To determine the permanency of the crimp in Dacron yarns, tests were also performed in which the yarn was processed and heat developed as previously described and thereafter immersed in warm water at a temperature of 140 F. under a tension of approximately 0.0014 gram per denier (a skein containing 40 turns was weighted with a 1.63 gram weight) and the length of the skein measured after specified periods of time. The skeins were then removed, patted dry with cleansing tissue, allowed to condition for one hour at a relative humidity of and a temperature of 70 F. and skein length determinations were made in air with the skeins, in each instance, weighted with a 1.63 gram weight.

The results of these tests are given in the following table:

Table V DEVELOPED AT 338 F.

Shrinkage (percent) Process Before After In Warm Water After Heat Heat Removal Develop- Develop- From ment ment 5 Min. 10 Min. Water DEVELOPED AT 393 F.

No. 7 1. 2 52. 8 49. 7 49. 1 47. 8 N0. 8 0.6 57. 1 51. 6 50. 9 50. 6 No. 9 1. 8 57. 1 53. 4 52. 8 51. 5 No. 10 1.8 49. 4 48. 5 47. 9 47. 5 No. 11. 2. 5 51. 9 48. 8 48. 2 48. 2

It will be seen that the crimp, in all instances, is quite permanent to warm water and that, based upon crimp retained, all processes except No. 10 wherein the yarn was passed cold about the blade and developed at 393 F., show at least some improvement over process No. 7. In other words, by the improved processes of this inven tion it is possible, in most instances, with Dacron yarns to Obtain better results by passing the yarn over the blade edge cold than it was previously possible to obtain by passing the yarn about the blade edge while at an elevated temperature.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

1. Apparatus for processing a running length of yarn comprising a yarn supply means, a first yarn advancing means to positively advance an end of yarn from said supply means along a linear path at a first selected linear rate, a second yarn advancing means to thereafter positively advance said end of yarn along said path at a second linear rate which is in excess of said first linear rate so that said yarn is stretched, heater means to heat said yarn in a portion of the yarn path between said first yarn advancing means and a point in the yarn path where the yarn is positively advanced by said second yarn advancing means so that the stretching of said yarn occurs in a heated segment thereof, a blade means, means including contact heater means proximate to but spatially separate from said blade means to heat said yarn in a portion I of the yarn path immediately preceding said blade means to guide said yarn about an edge of said blade means in an angular path with said edge positioned at the apex of the angle in the yarn path, a yarn advancing means to receive said yarn following its contact with said edge and to positively advance the same along the yarn path at a third selected linear rate, and means to thereafter collect said yarn.

2. The combination of claim 1 wherein said means to guide said yarn about said edge comprises first and second rolls disposed in proximate spaced relationship to each other, said rolls being positioned with respect to said blade such that said blade extends into the space between said rolls and said edge is positioned in close proximity to the peripheral surface of said first roll.

3. The combination of claim 2 including means to heat at least an annular portion of the peripheral surface of said first roll.

4. The combination of claim 2 including means to drive said first and second rolls such that they have different surface speeds.

5. The combination of claim 2 wherein the longitudinal axis of said edge, the axis of rotation of said first roll and the axis of rotation of said second roll are each at an angle to each other so that said yarn is guided by said rolls in such a manner that it approaches and departs .18 said edge, in each instance, at an angle to the normal in a plane parallel to said edge.

6. Apparatus for processing a running length of yarn comprising a first yarn advancing means to positively advance an end of yarn along a linean' path at a first selected linear rate, a second yarn advancing means including at least one driven roll to thereafter positively advance said end of yarn along said path at a second linear rate which is in excess of said first linear rate so that said yarn is stretched, a blade means having a sharp edge, said blade means being so positioned that said edge is in close proximity to the surface of said roll, guide means to guide said yarn from said roll about said edge. in an acutely angular path with said edge disposed at the apex of the angle in the yarn path, a yarn advancing means to receive said yarn following its contact with said edge and to positively advance the same along the yarn path at a third selected linear rate, and means to heat at least a portion of the peripheral surface of said roll, said roll being so positioned that it is the first element of said second yarn advancing means contacted by said yarn so that said roll serves to heat a segment of said yarn between said first yarn advancing means and a point where it is positively advanced by said second yarn advancing means and so that the stretching of said yarn occurs in said heated segment, said roll also serving to heat said yarn in a segment of the yarn path immediately preceding the point Where said yarn contacts said blade edge so that said yarn is at an elevated temperature at the time it passes about said blade edge.

7.The combination of claim 6 wherein said guide means is an unheated roll positioned adjacent one face of said blade, and including means to drive said unheated roll with a surface speed different from the linear speed of the yarn in surface contact therewith.

8. In a yarn processing apparatus, the combination with said yarn along said path at a second linear rate, a blade member, and means to guide said yarn, in a portion of the yarn path between said first and second yarn advancing means, about an edge of said blade member in an angular path with said edge disposed at the apex of the angle in the yarn path, a roll, means to guide said yarn, in a portion of the yarn path between said blade and said second yarn advancing means, into sliding frictional contact with the surface of said roll, and means to drive said roll with a surface speed different from thelinear speed of the yarn in contact with said roll to thereby partially determine and regulate the tension in the yarn passing about said edge.

9. In a yarn processing apparatus, the combination with a blade means having a sharp edge, yarn heating means disposed adjacent said edge of said blade, and means to transport an end of yarn under tension through a linear path, said path being such that said yarn is passed into effective relationship with said yarn heating means and immediately thereafter aboutsaid edge of said blade means in an angular manner with said edge being disposed at the apex of the angle in the yarn path, of a heat conducting metal roll positioned in close proximity to one face of said blade means, and guide means to guide the yarn in a partial wrap about said roll immediately following its contact with said edge to thereby cool said yarn.

10. Apparatus according to claim 9 including means to drive said roll with a surface speed different from the linear speed of the yarn in contact therewith.

11. Yarn processing apparatus comprising in combinain proximate spaced relationship to each other, and a blade member extending between said two rolls such that said yarn in passing from said first roll to said second roll passes in an acutely angular path about an edge of said blade with said edge disposed at the apex of the acute angle in the yarn path.

12. The combination of claim 11 including means to drive at least one of said rolls such that it has a surface speed different from the linear speed of the yarn in contact therewith.

13. The combination of claim 11 including means to heat at least a portion of the peripheral surface of said first roll.

14. In a yarn processing apparatus, the combination with a blade means having a sharp edge, and means to transport an end of yarn under tension through linear path about said edge, of guide means to guide said yarn about said edge such that the yarn approaches and departs said edge, in each instance, at an angle to the normal in a plane parallel to said edge, said guide means comprises first and second rolls disposed in proximate spaced relationship to each other, said rolls being positioned with respect to said blade such that said blade extends into the space between said rolls, the axis of rotation of said first roll being at an angle to the longitudinal axis of said edge, and the axis of rotation of said second roll being at an angle to the longitudinal axis of said edge and to the axis of rotation of said first roll.

15. A process for elasticizing a thermoplastic yarn which comprises heating said yarn to a temperature below the melting point thereof but not more than about 270 F. below its melting point, stretching said yarn while it is at an elevated temperature, and therefore passing said yarn in an acutely angular path about the edge of a blade member, the temperature of said yarn at the time it is passed to said edge being at least about 200 F.

16. A process for elasticizing a partially crystalline thermo plastic yarn that has been cold drawn a near maximum extent consistent with yarn uniformity which process comprises passing a running length of said yarn through a linear path under tension, heating said yarn in one portion of the yarn path to a temperature below the melting point thereof but not more than about 180 F. below its melting point, stretching the hot yarn not more than about 15% of its original length, and thereafter passing said yarn in an acutely angular path about the edge of a blade member, the temperature of said yarn at the time it is passed to said edge being at least about 200 F.

17. A process according to claim 16 wherein the yarn is a polyhexamethylene adipamide nylon yarn, the temperature of the yarn during the hot stretching opertaion is from about 280 F. to 390 F., and the temperature of the yarn at the time it is passed to the blade edge is from about 280 F. to 360 F.

18. A process according to claim 16 wherein the yarn is a polycaprolactam nylon yarn, the temperature of the yarn during the hot stretching Operation is from about 240 F. to 320 F., and the temperature of the yarn at the time it is passed to the blade edge is from about 240 F. to 340 F.

19. A process according to claim 16 wherein the yarn is a polyethylene glycol-terephthalate yarn, the temperature of the yarn during the hot stretching operation is from about 270 F. to 430 F., and the temperature of the yarn at the time it is passed to the blade edge is from about 280 F. to 425 F.

20. A process for elasticizing a partially crystalline thermoplastic yarn that has been cold drawn a near maximum extent consistent with yarn uniformity which process comprises passing a running length of said yarn through a linear path under tension, heating said yarn in one portion of the yarn path to a temperature not less than about 215 F. but below its melting point, stretching the hot yarn not more than about 15% of its original length, cooling the 20 yarn, and thereafter passing said yarn in an acutely angular path about the edge of an unheated blade member.

21. A process according to claim 20 wherein the yarn is a polyethylene glycol-terephthalate yarn, and the temperature of the yarn during the hot stretching operation is from about 370 F. to 430 F.

22. Yarn processing apparatus comprising, in combination, means to transport a running length of yarn under tension through a linear path, a first roll positioned in the yarn path such that the yarn operatively engages the peripheral surface of said roll, a second roll positioned in said yarn path in proximate spaced relationship to said first roll such that the yarn operatively engages the peripheral surface of said second roll through a partial wrap, and a blade member having an edge operatively positioned intermediate said two rolls so that said yarn in passing from said first roll to said second roll passes about said edge in an acutely angular manner with said edge disposed at the apex of the angle in the yarn path.

23. Apparatus according to claim 22 including means to heat at least a portion of the peripheral surface of said first named roll so that said yarn is operatively at an elevated temperature as it passes about said blade edge, and wherein said second named roll is an unheated roll which serves to cool said yarn following its passage about said edge.

24. Apparatus according to claim 23 including means to drive said unheated roll such that it has a surface speed less than the linear rate of movement of the yarn in surface contact therewith.

25. In a process for elasticizing a partially crystalline thermoplastic yarn which has been cold drawn a near maximum extent consistent with yarn uniformity, said process including the steps of passing a running length of said yarn through a linear path under tension, heating said yarn in one portion of the yarn path to a temperature of at least about 200 F. but below the melting point of the yarn, and passing the hot yarn about the edge of a blade member in an acutely angular path with the edge of said blade member disposed at the apex of the angle, the improvement which comprises stretching said yarn not more than about 15% of its original length before it is passed about said blade edge but while it is at an elevated temperature and within said one portion of the yarn path.

26. A process for elasticizing polyester yarns which comprises heating the yarn to a temperature not less than about F. below the sticking temperature of the yarn but not above the sticking temperature of the yarn, stretching the heated yarn beyond its elastic limit but insufficient to break the same, cooling the yarn and thereafter passing the same through a linear path having an acutely angular portion.

27. A method for elasticizing fully drawn nylon yarn which method comprises heating the yarn to a temperature of at least about F. but not more than about 410 F., stretching the heated yarn sufiiciently to result in its having a decreased elongation to break but to an insufficient extent to rupture the yarn, and thereafter pass ing the yarn under tension through a linear path having an acutely angular portion, while said yarn is heated to a temperature from about 240 F. to 340 F.

28. In a process for elasticizing a fully drawn thermoplastic yarn wherein the yarn is continuously passed in an angular path over the sharpened edge of a blade member while under tension, said edge being disposed at the apex of an acute angle formed between the path of delivery of the yarn to said edge and the path of withdrawal of the yarn from said edge, the improvement which comprises, as a preliminary step, hot stretching said yarn beyond its elastic limit to increase its modulus of elasticity and its brittleness and to decrease its characteristic elongation to break.

29. An improved process according to claim 28 Wherein the degree of hot stretching and the temperature of the yarn during the hot stretching operation are such as to provide the yarn with a modulus of elasticity and brittleness which are substantially the maximum possible and a characteristic elongation to break which is substantially the minimum possible for the particular yarnbeing processed.

30. An improved process according to claim 29 wherein the starting yarn is a molecularly oriented polyamide yarn, the temperature of the yarn during the hot stretching operation is from about 180 to 410 F. and the degree of hot stretching is from about to 15%.

31. An improved process according to claim 29 wherein the yarn is a polyester yarn.

32. An improved process according to claim 31 wherein the starting yarn is a molecularly orientated polyethylene glycol-terephthalic acid ester yarn, the temperature of the yarn during the hot stretching operation is from about 300 to 455 F. and the degree of hot stretching is from about 4 to 7% 33. In an apparatus for processing a running length of yarn, the combination with a blade member having an edge and means to transport a running length of yarn under tension through a linear path passing about said edge in an acutely angular manner with said edge positioned at the apex of the acute angle in the yarn path, of heating means to heat said yarn in a portion of the yarn path preceding said acute angle, and means to stretch the hot yarn a selected amount prior to its being passed about said edge comprising a first yarn advancing means to transport the yarn at a first linear rate, and a second yarn advancing means to transport the yarn at a linear rate in excess of that at which it is transported by said first yarn advancing means, said second yarn. advancing means comprising at least one roll having a yarn engaging peripheral surface and said heating means comprising a heater to elevate the temperature of at least the peripheral surface of said roll, said blade member being in close proximity with the heated peripheral surface of said roll so that the yarn, as a result of its contact with the surface of said roll, is at an elevated temperature at the time it passes through said acute angle.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,273 Dreyfus Dec. 9, 1941 2,668,430 Laros Feb. 9, 1954 2,875,502 Matthews et al. Mar. 3, 1959 2,926,065 Coplan et a1 Feb. 23, 1960 FOREIGN PATENTS 522,045 Belgium Feb. 10, 1954 558,297 Great Britain Nov. 29, 1945 

1. APPARATUS FOR PROCESSING A RUNNING LENGTH OF YARN COMPRISING A YARN SUPPLY MEANS, A FIRST YARN ADVANCING MEANS TO POSITIVELY ADVANCE TO AN END OF YARN FROM SAID SUPPLY MEANS ALONG A LINEAR PATH AT A FIRST SELECTED LINEAR RATE, A SECOND YARN ADVANCING MEANS TO THEREAFTER POSITIVELY ADVANCE SAID END OF YARN ALONG SAID PATH AT A SECOND LINEAR RATE WHICH IS IN EXCESS OF SAID FIRST LINEAR RATE SO THAT SAID YARN IS STRETCHED, HEATER MEANS TO HEAT SAID YARN IN A PORTION OF THE YARN PATH BETWEEN SAID FIRST YARN ADVANCING MEANS AND A POINT IN THE YARN WHERE THE YARN IS POSITIVELY ADVANCED BY SAID SECOND YARN ADVANCING MEANS SO THAT THE STRETCHING OF SAID YARN OCCURS IN A HEATED SEGMENT THEREOF, A BLADE MEANS, MEANS INCLUDING CONTACT HEATER MEANS PROXIMATE TO BUT SPATIALLY SEPARATE FROM SAID BLADE MEANS TO HEAT SAID YARN IN A PORTION OF THE YARN PATH IMMEDIATELY PRECEDING SAID BLADE MEANS TO GUIDE SAID YARN ABOUT AN EDGE OF SAID BLADE MEANS IN AN ANGULAR PATH WITH SAID EDGE POSITIONED AT THE APEX OF THE ANGLE IN THE YARN PATH, A YARN ADVANCING MEANS TO RECEIVE SAID YARN FOLLOWING ITS CONTACT WITH SAID EDGE AND TO POSITIVELY ADVANCE THE SAME ALONG THE YARN PATH AT A THIRD SELECTED LINEAR RATE, AND MEANS TO THEREAFTER COLLECT SAID YARN. 